New layered zeolitic imidazolate frameworks, methods of preparation & uses thereof

Abstract

The invention relates to a new layered zeolitic imidazolate frameworks, methods of preparation & uses thereof.

Description

[0001] NEW LAYERED ZEOLITIC IMID AZOLATE FRAMEWORKS, METHODS OF PREPARATION & USES THEREOF

[0002] Field of the Invention

[0003] The present invention pertains generally to the field of layered ZIF materials.

[0004] Background of the Invention

[0005] Zeolitic imidazolate frameworks (ZIFs) represent an important class of porous materials belonging to the broader family of metal-organic frameworks (MOFs) (Tan et al., 2018, Chemical Society Reviews, 47(6),.2130-2144'). ZIFs are often formed using transition metal node (e.g., zinc or cobalt) linked by imidazolate-based organic ligands and are constructed from tetrahedra M(Im)4, where M stands for metal ions (e.g., Zn2+, Co2+), and Im is an imidazolate ligand. The metal ions are bridged tetrahedrally with a near 145° bond angle, mimicking the bonding arrangement of zeolites (Banerjee et al., 2008, Science, 319(5865), 939-943). The combination of coordination chemistry and zeolite-topology endows ZIFs with unique properties, including tunable synthesis by a wide range of synthesis techniques (Chen etal., 2014, Journal of Materials Chemistry A, 2(40), 16811-16831; Kouser et al., 2022. Journal of Porous Materials, 29(3), 663-681), high surface area (Banerjee et al., 2009, Journal of the American Chemical Society, 131(11), 3875-3877; Ighalo et al., 2022, Journal of Industrial and Engineering Chemistry, 105, 34-48) high thermal stability (Healy et al., 2020, Coordination Chemistry Reviews, 419, 213388), molecular selectivity (Pimentel et al., 2014, ChemSusChem, 7(12), 3202-3240).

[0006] These properties make ZIFs attractive in a variety of applications, e.g., molecular separation (Ighalo et al., 2022, supra; Pimentel et al., 2014, supra; Wang et al., 2008, Nature, 453(7192), 207-211; Ma et al., 2018, Science, 361(6406), pp.1008-1011), drug delivery (Akhtar et al., 2024, Advances in Colloid and Interface Science, 103184-1011), sensing (Zhang et al., 2020, Microchimica Acta, 187, 1-23) and catalysis (Duan et al., 2018, Chemical Engineering Journal, 334, 1477-1483; Bhattacharjee et al., 2014, Catalysis Surveys from Asia, 18, .101-127).

[0007] ZIFs are traditionally prepared in 3D structures. One of the most studied ZIF is ZIF-8 which adopts the sodalite (SOD) topology. Duan et al., 2023, Journal of membrane Science letters, 3, 100045 discloses the preparation of ZIF-8 membranes by direct assembly of nanosheets from bottom-up synthesis growth solution in presence of sodium dodecyl sulfate wherein the obtained material has a typical structure of a ZIF-8 as characterized by X-ray diffraction.

[0008] However, a few two-dimensional (2D) ZIFs in layered morphology have been reported. ZIF-L consists of 2D layers which are separated by coordinated and free 2-methylimidazolium (Hmlm)ligands (Chen et al., 2013, Chemical Communications, 49(82), 9500-9502; Feng et al., 2021, Coordination Chemistry Reviews, 4321, 213677), Zn2(benzimidazole)4 (Peng et al., 2014, Science, 346(6215), 1356-1359') and Co4(benzimidazole)i6 (Jayaramulu et al., 2018, Advanced Science, 5(11), 1801029) consist of 2D layers held together by weak van der Waals interactions. Lotsch and coworkers (Junggeburth et al., 2013, J. Am. Chem. Soc., 135) showed that a cationic surfactant, cetyltrimethylammonium bromide (CTAB), can be used to template mesostructured ZIFs. These materials have a thickness of about a few hundreds of nanometers (for the case of ZIF-L) to a few micrometers (for other layered ZIFs) and have to be exfoliated in order to obtain thin sheets. WO 2024 / 104957 discloses the preparation of 2D ZIF films on graphitic substrates and those methods rely on the presence of 2D substrates to anchor the registry of the ZIF material to make membranes (bottom-up approach) and in the absence of which it is impossible to obtain a 2D material.

[0009] Sodium dodecyl sulfate (SDS) has been used for the synthesis of ZIF-8 / ZIF-67 nanoplatelets (Wan, et al., 2020, Chemical Communications, 56(31), 4316-4319; Duan etal., 2023, supra . However, in these nanoplatelets, this surfactant is used as a capping agent for morphology control of the final crystal by inhibiting out-of-plane crystal growth of ZIF-8 / ZIF-67, wherein the surfactant attaches on the surface of the crystals and prevent their growth to form large crystals. As a result, the surfactant remains at the surface of the structure, and a thick isotropic crystal with a nonlayered morphology is achieved.

[0010] Compared with 3D ZIFs, 2D ZIFs offer unique advantages from sheet-like morphology, e.g., a high surface-to-volume ratio, abundant surface-active sites and the ability to be exfoliated to thin nanosheets. These properties are beneficial for the construction of ultrathin selective membranes (Peng et al., 2014, supra; Yu etal., 2022, Journal of Materials Chemistry A, 10(29), 15390-15394; Jia et al., 2024, Separation and Purification Technology, 338, 126589) for the preparation of efficient adsorbents (Nasir et al., 2018, J. Mol. Liq., 250, 269 277; Huang et al, 2021, Science of The Total Environment, 785, 147382) and drug delivery systems (Song et al, 2020, ChemMedChem, 15(5), 416-419) and for producing ZIF-derived catalysts (Sun et al, 2023, ACS Sustainable Chemistry & Engineering, 11(31), 11625-11634) electrodes (Gao et al, 2021, Analytical and Bioanalytical Chemistry, 413, 7485-7494; Wang et al, 2018, Advanced Functional Materials, 28(5), 1705048).

[0011] Despite the large number of ZIF structures, only a few have been reported in 2D morphology. This is due to the tetrahedral coordination environment of the metal node which promotes structure propagation in three dimensions unless the coordination can be somehow terminated.Therefore, given the unique advantages of a 2D morphology conferring sheet-like morphology unique properties over 3D ZIF structures, there is a need for developing new layered ZIF materials.

[0012] Summary of the Invention

[0013] A general object of this invention is to provide new layered ZIF materials and a cost-effective process for the preparation of the same.

[0014] It has been unexpectedly found that it is possible to prepare in a very rapid and simple manner ZIF materials with sheet-like morphology with a thickness varying from a few nanometers to 100-200 nm and lateral size of a few micrometers. In particular, it was unexpectedly found that the combined use of a dilute metal precursor concentration with an anionic surfactant as a structure directing agent (SDA) in the preparation of ZIF materials favors the construction of layered ZIF structure spaced by anionic surfactant micelles, leading to the incorporation of anionic surfactant into the layered space and holding together the unit-cell-thick ZIF layers as schematized in Figure 2f. As opposed to known 2D ZIF materials which have properties similar to the parental 3D ZIF counterparts (except for the fact that they have sheet-like morphology and thus have properties obtained from the sheet-like form, e.g., high surface-to-volume ratio, abundant surface-active sites, the ability for the easy construction of thin films / membranes), the layered ZIF material of the invention has surprisingly a completely different structure from the parental material.

[0015] It is advantageous to provide ZIF materials with sheet-like morphology with an aspect ratio (ratio of the length to the width) higher than 10 (e.g., 20-500) and a large lateral size (i.e. larger than 1’000 nm) which are useful for making compact films and membranes.

[0016] One of the specific objects of this invention is to provide ZIF materials with sheet-like morphology leading to a high surface-to-volume ratio and ability to be exfoliated into thin nanosheets.

[0017] It is advantageous to provide a facile and scalable method for the preparation of layered ZIF materials.

[0018] It is advantageous to provide a method for the preparation of two-dimensional layered ZIF materials allowing the incorporation of anionic surfactants in the structure of the ZIF material and intercalating the ZIF layers.

[0019] It is advantageous to provide a method for the preparation of two-dimensional layered ZIF materials having a pore opening which is useful for H2 / CO2 separation (e.g. 0.29 - 0.33 nm).Objects of this invention have been achieved by providing a method of preparation ZIF materials with sheet-like morphology with a thickness varying from a few nanometers to 100-200 nm and lateral size of a few micrometers.

[0020] It is advantageous to provide ZIF materials forming large lateral size (e.g. larger than 1’000 nm) and aspect ratio higher than 10 (e.g. 20-500) nanosheets for the preparation of molecular sieving membranes with energy-efficient gas separation properties.

[0021] It is advantageous to provide 2D ZIF membranes with a H2 permeance at 200°C from of 2 * 10'8to about 3.5* 10'8mol m'2s'1pa'1.

[0022] It is advantageous to provide 2D ZIF membranes with selectivities for H2 over CO2, CH4, and N2 greater than 20 (e.g. 30), greater than 50 (e.g. 400), and greater than 50 (e.g. 200), respectively, at 200°C.

[0023] It is advantageous to provide 2D layered ZIF membranes presenting high stability even under humidified atmosphere at high temperature (e.g. 200°C).

[0024] Objects of this invention have been achieved by the provision of new layered ZIF materials according to the invention and their use for the the preparation of molecular sieving membranes. Disclosed herein is a method for the preparation of a layered zeolitic imidazolate framework (ZIF) material, said method comprising the steps of:

[0025] a) Providing an anionic surfactant solution of the metal ion precursor under continuous stirring wherein the molar ratio of metal ions to anionic surfactant is from about 0.5 to about 4 (e.g. typically from about 0.5 to about 2 such as from about 1 to about 2), under continuous stirring;

[0026] b) Providing a separate organic ligand solution in aqueous solution under continuous stirring; c) Adding the anionic surfactant solution of the metal precursor to the said organic ligand solution to form a reaction mixture, wherein the molar ratio of organic ligand to the metal is from about 8.5 to about 150, from about 10-150, typically from 20-150, preferably from 30 to about 150, preferably by from 30-100, typically from 35-100;

[0027] d) Leaving the formed mixture under stirring until a layered ZIF is formed;

[0028] e) Collecting the obtained ZIF material.

[0029] Two-dimensional layered zeolitic imidazolate framework (ZIF) material can be filtered through a porous support under vacuum filtration at room temperature as described herein for obtaining films.Also disclosed herein is a two-dimensional layered ZIF material having a sheet-like morphology with an aspect ratio (ratio of the length to the width) higher than 10 (e.g., 20-500) and a large lateral size (i.e. larger than 1’000 nm).

[0030] Also disclosed herein is a porous substrate coated with a film comprising a two-dimensional layered zeolitic imidazolate framework (ZIF) material of the invention.

[0031] Also disclosed herein is a selective gas filter comprising a membrane comprising a porous substrate coated with a two-dimensional layered ZIF film from a two-dimensional layered ZIF material of the invention.

[0032] Also disclosed herein is the use of a gas selective filter of the invention for separating H2 and CO2 comprising a membrane comprising a porous substrate coated with two-dimensional layered ZIF film according to the invention.

[0033] Other features and advantages of the invention will be apparent from the claims, detailed description, and figures.

[0034] Brief Description of the drawings

[0035] Figure 1 presents SEM images of ZIF-S-Zn nanosheets growth (material of the invention synthesized and sampled as described in Example 1 at room temperatures over synthesis time: a:

[0036] 1 h; b: 2 h and c: 4 h. Scale bars represent 5 pm.

[0037] Figure 2 presents the characterization of ZIF-S-Zn synthesized at room temperature in 4 h as described in Example 2. a: SEM image showing the typical morphology and size of the synthesized nanosheets; b: TEM image showing the well-faceted square morphology of the nanosheet; c: corresponding SAED pattern of the nanosheet shown in b; d: XRD analysis of the ZIF-S-Zn nanosheet powder; e: FTIR spectra of the layered ZIF-S-Zn material and its comparison with that of ZIF-8 and SDS; f: Structure model of the layered ZIF-S-Zn material solved by the Micro-ED technique presenting a stacking arrangement with the thickness of a single unit cell wherein the anionic surfactant chains would be intercalated; g: Comparison ofJH solid-state NMR spectra of the ZIF-S-Zn material with that of 2 precursors (2-metylimidazole and SDS; h:JH-13C HETCOR solid-state NMR spectrum of the layered Zn-ZIF material, i:

[0038]

[0039] EXSY solid-state NMR spectrum of the layered ZIF-S-Zn material.

[0040] Figure 3 presents the characterization of ZIF-S-Co material synthesized at room temperature in 1 h as described in Example 2. a: SEM image showing the typical morphology and size of the synthesized nanosheets; b: TEM image showing the well-faceted square morphology of the nanosheet; c: the corresponding SAED pattern of the nanosheet shown in (b); d: powder XRDpattern of the ZIF-S-Co and its comparison with that of the ZIF-S-Zn; e: FTIR spectra of the ZIF-S-Co and its comparison with that of the ZIF-S-Zn; f: powder XRD patterns of ZIF-S-Co at different temperatures. The data was generated by in-situ heating while measuring XRD.

[0041] Figure 4 illustrates the phase change by topotactical condensation as described in Example 4. a:

[0042] Structure model of the layered ZIF-S-Zn material view along the a-axis (surfactant is not shown for simplicity); b: Structure model of ZIF-8 material view along the a-axis, illustrating the topotactic condensation of the layered ZIF-S-Zn to ZIF-8; c: powder XRD patterns of the layered ZIF-S-Zn material at different temperatures with in-situ heating, d: TGA data of the layered ZIF-S-Zn powder material.

[0043] Figure 5 characterizes the transformation of the material of the invention ZIF-S-Zn into ZIF-8 upon ethanol washing at room temperature by topotactical condensation as described in Example 4 as shown by SEM image (a) and corresponding XRD pattern (b) of ZIF-S-Zn (1) after washing with ethanol at room temperature. XRD curve (2) represents ZIF-8 reference.

[0044] Figure 6 characterizes the ZIF-S-Zn nanosheets as described in Example 5 after deposition on porous PBI support, after centrifugation at 10’000 rpm for 10 min (a) and after sedimentation for 24 h (b) by AFM images; c: height profiles of the nanosheets shown in (a) and (b); d: SEM image of the porous PBI supports; e: Top-view SEM image of the ZIF-S-Zn; (f) Single gas permeation tests performed on the as-prepared ZIF-S-Zn nanosheet membrane to examine its molecular sieving properties.

[0045] Figure 7 characterizes the ZIF-S-Co nanosheets as described in Example 5 after deposition on porous PBI support, after centrifugation at 10’000 rpm for 10 min (a) and after sedimentation for 24 h (b) by AFM images; c: the height profiles of the nanosheets shown in a and b s; d: Top-view SEM image of the prepared ZIF-S-Co membrane; e: cross-section cross section SEM image of the prepared ZIF-S-Co membrane; f: stability test of the ZIF-S-Co material in humid N2 ( ~ 2.5 mol% water vapor) at 200°C; g: single gas permeation results showing EE permeance as a function of testing temperature and the corresponding H2 / CO2, H2 / CH4 and H2 / N2 ideal selectivities; h: membrane stability test using a 50 / 50 mol% H2 / CO2 gas mixture with ~ 1.5 mol% water vapor at 200°C.

[0046] Figure 8 presents the characterization of the material of the invention ZIF-S-Co synthesized using molar ratios of the reactants Co(NO3)2.6H2O : Hmlm : SDS = 1 : 36 : 1.1, as described in Example 8. SEM image (a) showed a nanoplatelet morphology similar to Example 1 and the corresponding XRD pattern (b) of the ZIF-S-Co (2) in this Example matches that of Example 1. XRD curve (1) represents ZIF-S-Co synthesized using molar ratios of reactants (Co(NO3)2.6H2O : Hmlm : SDS = 1 : 72 : 0.57) from Example 1.Figure 9 presents the characterization of the obtained comparative material (which has an unknown structure) obtained with similar molar ratios of reactants (Co(NO3)2.6H2O : Hmlm : SDS = 1 : 8 : 1) than those of the material disclosed in Duan et al., 2023, supra, but with more dilute precursor concentrations (10 times more dilute), as described in Example 8. SEM image (a) showed a nanoparticle morphology, which is different from the nanoplatelet morphology of the material in this invention and the material disclosed in Duan et al., 2023, supra. The corresponding XRD pattern (b) of the material (1) does not match neither that of the material in this invention nor the ZIF-67 material. The synthesized material has an unknown structure, and a low crystallinity. XRD curve (2) represents ZIF-67 reference.

[0047] Detailed description of embodiments of the invention

[0048] The expression “ZIF metal precursor solution” comprises metal ions such as Zn2+or Co2+.

[0049] The expression “an organic ligand” refers to a ligand for the formation of a ZIF and includes 2-methylimidazole (Hmlm or mlm), imidazole (Im), benzimidazole (bzlm), imidazole-2-carboxaldehyde (allm), 2-nitroimidazole (nlm), 5-azabenzimidazole (5-abIm). Various layered ZIFs could be prepared according to a method of the invention, including ZIF-7 (Zn(BzIm)2, ZIF-8 Zn(mlm)2, ZIF-9 Co(blm)2, ZIF-10 Zn(Im)2, ZIF-22 Zn(5ablm)2, ZIF-65 Co(nlm)2and ZIF-90 Zn(allm)2.

[0050] The expression “nanosheet” refers to crystals which have a two-dimensional morphology. Typically, nanosheets of the material of the invention are crystals which have a two-dimensional morphology with thickness of 1 to 100 nm.

[0051] A “porous substrate” in relation to the context of the invention refers to a support which porosity is from about 20% to about 40% at room temperature as determined by standard techniques determining the pore density such as commonly measured by High-resolution scanning electron microscopy. Suitable porous substrates of a film or membrane of the invention comprise for example polybenzimidazole (PBI), polyethersulfone (PES), polyimide (PI), Polyvinylidene fluoride (PVDF).

[0052] The expression “topotactic condensation” is a solid-state reaction where a crystalline precursor (often layered silicates) condenses at high temperature to form an ordered three-dimensional structure (such as zeolites). In such a process, the layered 2D material is condensed to a 3D material by bridging the layers (Marler etal., 2012, European Journal of Mineralogy, 24(3), 405-428) Disclosed herein is a method for the preparation of a two-dimensional layered zeolitic imidazolate framework (ZIF) material, said method comprising the steps of:a) Providing an anionic surfactant solution of the metal ion precursor under continuous stirring wherein the molar ratio of metal ions to anionic surfactant is from about 0.5 to about 4 (e.g. typically from about 0.5 to about 2 such as from about 1 to about 2), under continuous stirring; b) Providing a separate organic ligand solution in aqueous solution under continuous stirring; c) Adding the anionic surfactant solution of the metal precursor to the said organic ligand solution to form a reaction mixture, wherein the molar ratio of organic ligand to the metal is from about 8.5 to about 150, from about 10-150, typically from 20-150, preferably from 30 to about 150, preferably by from 30-100, typically from 35-100;

[0053] d) Leaving the formed mixture under stirring until a layered ZIF is formed;

[0054] e) Collecting the obtained ZIF material.

[0055] According to a particular embodiment, the method is carried out at room temperature (for example, typically from about 22°C to 28°C).

[0056] According to a particular embodiment, the anionic surfactant solution of the metal ion precursor can be prepared by i) providing an anionic surfactant in aqueous solution under continuous stirring for about 5 min to about 10 min and ii) adding a metal precursor solution to the anionic surfactant in a molar ratio metal ions to anionic surfactant from about 1 to about 2, under continuous stirring to form said anionic surfactant solution of the metal precursor.

[0057] According to another particular embodiment, the anionic surfactant is selected from Sodium dodecyl sulfate (SDS), Sodium lauryl ether sulfate, Sodium myreth sulfate, Sodium lauroyl sarcosinate, sodium dodecyl benzenesulfonate and sodium stearate.

[0058] According to a further particular embodiment, the anionic surfactant is dodecyl sulfate (SDS). According to a particular embodiment, the metal precursor solution comprises metal ions selected from Zn2+and Co2+.

[0059] According to another particular embodiment, the molar ratio of metal ions to anionic surfactant is from about 1 to about 3.

[0060] According to a particular embodiment, the anionic surfactant solution of the metal precursor is added to the said organic ligand solution such that the metal precursor: anionic surfactant molar ratio is from about 1 :0.5 to 1:1.

[0061] According to a particular embodiment, the anionic surfactant solution of the metal precursor is added to the said organic ligand solution such that the molar ratios of organic ligand to the metal are from about 30 to about 100 to form a reaction mixture.According to a particular embodiment, the anionic surfactant solution of the metal precursor is added to the said organic ligand solution such that the metal precursor: anionic surfactant: organic ligand molar ratios are from about 1 : 1 : 72 to about 1 : 0.5 : 72 to form a reaction mixture.

[0062] According to a particular embodiment, the anionic surfactant solution of the metal precursor is added to the said organic ligand solution such that the metal precursor: anionic surfactant: organic ligand molar ratio is about 1 : 1.1 : 36 to form a reaction mixture.

[0063] According to a particular embodiment, the reaction mixture is left under continuous stirring until crystals with square and nanoplatelet morphology are formed which is indicative of the formation of layered ZIFs. This can be monitored by imaging a drop of said mixture on a silicon wafer by scanning electron microscopy (SEM). Typically, reaction mixture lasts for about 15 minutes to about 4 hours (e.g. from about 1 or 2 hours up to 4 hours). For example, for layered ZIF-8 (ZIF-S-Zn) the used reaction mixture was about 2-4 hours and 0.5-1 h for layered ZIF-67 (ZIF-S-Co). According to a particular embodiment, the organic ligand is selected from benzimidazolate and 2-methylimidazolate (2mlm).

[0064] According to a particular embodiment, the obtained ZIF material is collected by centrifugation, typically at 10’000 rpm for about 5 to 15 min (e.g. 40 min).

[0065] According to a particular embodiment, the obtained ZIF material is subjected to a drying step for example in a convection oven (e.g. for about 12h) before storage.

[0066] According to a particular embodiment, is provided a two-dimensional layered ZIF material obtainable from a method of the invention.

[0067] According to a particular embodiment, is provided a two-dimensional layered ZIF material having a sheet-like morphology with an aspect ratio (ratio of the length to the width) higher than 10 (e.g., 20-500) and a large lateral size (i.e. larger than 1’000 nm).

[0068] According to a particular embodiment, the two-dimensional layered ZIF material having a sheetlike morphology with a thickness of approximately 5-20 nm (e.g. 10 nm).

[0069] According to a particular embodiment, the layered ZIF materials has a pore opening which is useful forEh / CCh separation (e.g. 0.29 - 0.33 nm).

[0070] According to a particular embodiment, the two-dimensional layered ZIF material having a sheetlike morphology has a structure belonging to the tetragonal lattice P421m space group.According to a further particular embodiment, the structure of the two-dimensional layered ZIF material comprises unit-cell-thick ZIF layers spaced by anionic surfactant micelles.

[0071] According to a further particular embodiment, the structure of the two-dimensional layered ZIF material is characterized by a molar ratio of the metal to the imidazolate compound from 0.35 to about 0.6, as determined by elemental analysis.

[0072] According to a further particular embodiment, the two-dimensional layered ZIF material undergoes topotactic condensation and forms its parent 3D ZIF material upon heating (e.g. to or above 200°C for ZIF-8 / ZIF-67).

[0073] According to a further particular embodiment, the two-dimensional layered ZIF material has the following unit cell parameters a = b = 16.82 A; c =24.5 A at room temperature.

[0074] According to a particular aspect is provided a two-dimensional layered ZIF material, wherein the metal ion is selected from Co+2and Zn+2.

[0075] According to a particular aspect is provided a two-dimensional layered ZIF material, wherein the anionic surfactant is selected from Sodium dodecyl sulfate (SDS), Sodium lauryl ether sulfate, Sodium myreth sulfate, Sodium lauroyl sarcosinate, sodium dodecyl benzenesulfonate and sodium stearate.

[0076] According to a particular aspect is provided a layered ZIF material, wherein the organic ligand is selected from benzimidazolate and 2-methylimidazolate.

[0077] According to a particular aspect is provided a film of a two-dimensional layered ZIF material wherein said film’s pore aperture is from 0.29 nm to 0.33 nm at temperatures from 150°C to 200°C. According to another aspect is provided a use of a two-dimensional layered ZIF for the manufacture of a selective gas filter.

[0078] According to another aspect is provided a support, in particular a porous substrate, coated with a film comprising a two-dimensional layered zeolitic imidazolate framework (ZIF) material of the invention.

[0079] According to a particular embodiment, the coating is carried out by filtration whereinthe material iin nanosheet morphology would deposit the sheets horizontally on the support and minimize pinhole defects, leading to gas selective filters.

[0080] According to a particular aspect, the two-dimensional layered zeolitic imidazolate framework (ZIF) film’s thickness is from about 100 nm to about 500 nm (e.g., about 300 nm).According to another particular aspect is provided a selective gas filter comprising a membrane comprising a porous substrate coated with a two-dimensional layered ZIF film from a two- dimensional layered ZIF material of the invention.

[0081] According to another particular aspect is provided a use of a selective gas filter of the invention for separating H2 and CO2.

[0082] According to a particular embodiment, gas filters according to the invention are useful for precombustion carbon capture, where the said gas selective filter would allow the separation of H2 over CO2 at elevated temperatures (e.g. 200°C).

[0083] According to another particular embodiment, the two-dimensional layered ZIF material can be used as adsorbents, pigments, electrocatalysts, electrode materials or supercapacitor material.

[0084] The invention having been described, the following examples are presented by way of illustration, and not limitation.

[0085] EXAMPLES

[0086] Materials

[0087] Zinc nitrate hexahydrate (Zn(NO3)2.6H2O, 98%), Cobalt nitrate hexahydrate (Co(NO3)2.6H2O, 98%), 2-Methylimidazole (Hmlm, C4H6N2, 99%), Sodium dodecyl sulfate (SDS, CH3(CH2)nOSO3Na, >98%) were purchased from Sigma- Aldrich. All the chemicals were used without further purification. PBI-AM Fumion® powder was obtained from Fumatech. Stainless- steel mesh (pore size 20 pm, Part number #325X2300TL0014) was obtained from TWP Inc. Example 1: Synthesis of layered ZIF-8 and ZIF-67 according to a method of the invention The method of the invention was applied to the synthesis of various ZIFs as described below at room temperature using aqueous solutions.

[0088] a) Providing an anionic surfactant in aqueous solution under continuous stirring Typically, an SDS solution was prepared by dissolving 0.045 g SDS in 100 mL ultrapure water (18.2 MQ cm) and mixed well by stirring.

[0089] b) Providing a metal precursor solution and adding said metal precursor solution to the anionic surfactant in a molar ratio metal ions to anionic surfactant from about 0.5 to about 4, in particular from 0.5 to 2, under continuous stirring to form an anionic surfactant solution of the metal precursor

[0090] Then, i) either a 0.0813 g Zn(NO3)2.6H2O or ii) 0.0786 g Co(NO3)2.6H2O was added into the SDS solution and the solution was mixed by stirring to form a SDS solution of Zn2+precursor or Co2+, respectively. In the present case, the molar ratio metal ions to anionic surfactant was 1:0.57.c) Providing a separate organic ligand solution in aqueous solution under continuous stirring In parallel, an Hmlm solution was prepared by dissolving 1.6 g Hmlm in 100 mL ultrapure water (18.2 MQ cm) and mixed by stirring. The two solutions were kept stir at room temperature until homogenous. The molar ratio of Hmlm to metal being 72.

[0091] d) Adding the anionic surfactant solution of the metal precursor to the said organic ligand solution such that the metal precursor: anionic surfactant molar ratios are from about 1 : 0.5 to about 1 :2

[0092] Next, the SDS solutions of Zn2+precursor or Co2+were quickly added to the Hmlm solution. The molar ratio of the reactants was Zn(NO3)2.6H2O : Hmlm : SDS = 1 : 72 : 0.57 or Co(NO3)2.6H2O : Hmlm : SDS = 1 : 72 : 0.57, respectively.

[0093] e) Leaving the formed mixture under stirring for a duration of 15 minute to 4 h until the mixture becomes cloudy and a layered ZIF is formed.

[0094] For the solution containing Zn2+precursor, reaction was carried out at room temperature for up to 4 hours. Samples were taken from the reaction mixture at 1 hour, 2 hours and 4 hours respectively, and drop-coated on silicon wafer for scanning electron microscopy (SEM) imaging to monitor the reaction process. The optimum reaction time was selected as 4 hours based on the SEM characterization which showed thin nanocrystals with well-faceted square morphology has been formed as described in Example 2.

[0095] SEM images in Figure 1 show progress of crystallization as a function of synthesis time. At short reaction time (1 h, Figure la), only aggregates could be observed from the synthesis solution. When reaction time was increased to 2 h (Figure lb), nanosheets with square morphology started to form. When reaction time was increased to 4 h (Figure 1c), nanosheets acquired well-faceted square morphology. Therefore, about 4h was estimated as optimum synthesis time in this case. For the solution containing Co2+precursor, reaction was carried out at room temperature for up to 1 hour since the kinetic of this reaction is faster than for the solution containing Zn2+precursor. Samples were taken from the reaction mixture at 5 min, 15 min, 30 min and 1 hour respectively, and drop-coated on silicon wafer for scanning electron microscopy (SEM) imaging to monitor the reaction process. The optimum reaction time was selected as 0.5 hours based on the SEM characterization which showed thin nanocrystals with well-faceted square morphology has been formed as described in Example 2.f) Collecting the obtained ZIF material

[0096] When the reaction was judged completed, the powdered ZIF materials (ZIF-S-Zn and ZIF-S-Co respectively) was retrieved by centrifuging at 10’000 rpm for 10 min and drying in a convection oven for about 12 h and stored. The supernatant was also collected for filtration purpose to make gas selective membranes. The nanosheet suspension will be then filtered through a porous support such that nanosheet would deposit horizontally on the support to lead togas selective membranes.

[0097] Example 2: Characterization of the synthesized layered ZIF-8 and ZIF-67 according to a method of the invention

[0098] The ZIF materials obtained in Example 1 were characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, Microcrystal Electron Diffraction (MicroED) and Solid-state NMR as described below.

[0099] Detailed characterizations were performed on the ZIF material obtained from the reaction of the solution containing Zn2+precursor (ZIF-S-Zn) synthesized in 4 h, as described above. SEM and TEM images of ZIF-S-Zn nanosheets reveal well-faceted square morphology (Figure 2a, b).

[0100] Selected area electron diffraction (SAED) pattern revealed a square 2D lattice in the in-plane direction (Figure 2c).

[0101] Powder X-ray diffraction (XRD) pattern recorded using a Bruker D8 Discover with CuKa radiation ( = 1.5406 A) confirmed that the material is distinct from ZIF-8 (Figure 2d). The presence of diffraction peak at a low angle (29 = 3.6°) suggests that the ZIF-S is likely layered.

[0102] Fourier-transform infrared (FTIR) spectroscopy performed on FT-IR- Spectrometer Spectrum Two (PerkinElmer) with an atmospheric vapor compensation feature (an advanced digital filtering algorithm) designed to compensate for CO2 and H2O absorptions in real time, also revealed a distinct spectrum than that of ZIF-8, with additional vibration modes appearing at wavenumbers of 2922.4, 2852.9, 1246.9, 1206.5, 622.8 and 583.5 cm’1. The comparison of the FTIR spectrum of ZIF-S with that of the SDS revealed that the additional vibration modes correspond to stretching modes of SDS. Peaks at 2922.4 and 2852.9 cm’1correspond to the stretching of the hydrophobic tails and the peaks at 1246.9, 1206.5, 622.8 and 583.5 cm’1correspond to the stretching of the -SO3-R head groups (Gao et al., 2010, Journal of colloid and interface science, 348(1), 167-176; Zhao et al., 1987, Colloid and Polymer Science, 265, 823-829). This implies that the surfactant chains were incorporated in the structure of the material.

[0103] Inductively-coupled plasma mass spectrometry (ICP-MS) analysis was performed on a NexION 350D inductively coupled plasma mass spectrometer on powder samples which were digested using microwave acid digestion with TraceMatal Grade HNO3 and revealed that ZIF-S does not containNa. This suggests that the anionic surfactant chain is likely coordinated in the structure and extraframework SDS is not present in the structure. ICP-MS has very high sensitivity and since ICP-MS did not show Na, it was concluded that the negative charges of anionic surfactant chains is compensated by other metals (Zn or Co), and therefore inferred that no extra-framework SDS is present.

[0104] Micro-ED technique was used to resolve the structure of the materials of the invention prepared as described above (ZIF-S). The structure could be solved using SHELXD (Sheldric et al., 2007, Acta Crystallogr. A, 64 (1), 112 122) in the space group P 2 m, which confirmed a layered structure. The structure was refined in SHELXL (Sheldrick et al., 2015, Acta Crystallogr. Sect. C Struct. Chem. 2015, 71 (1), 3-8. https: / / d0i.0rg / l 0.1107 / S2053229614024218 using the kinematical scattering approximation. Geometrical restraints to the ligands were added to regularize the geometry, as well as restraints on the displacement parameters.

[0105] Due to limited data, only the layers could be modelled. The asymmetric unit of the model consists of three Zn atoms, 2 complete ligand molecules and two half ligand molecules, which yields a chemical formula Zm.75(N2C4H5)3. This formula leaves a charge deficiency. There should be an added fragment corresponding to half negative charge per asymmetric unit. The chemical nature of this added charge could not be determined unambiguously with the 3D-ED data. However, from material chemistry view, the positively charged ZIF layers would be balanced by coordination with negatively charged dodecyl sulfate ions. This is also supported by the ICP analysis which suggests no Na is present in the structure, meaning that the dodecyl sulfate ions must be balanced by Zn metal centers. Therefore, the formula for ZIF-S-Zn was assigned as Zni.7s(N2C4H5)3(C 12^5804)0.5. The unit cell parameters of the material were determined to be a = b = 16.43 A; c=23.4 A at 77 K and a = b = 16.82 A; c=24.5 A at room temperature. A view of the structure along the a-out-of-plane is shown in Figure 2f. Surfactant chains are not shown for simplicity. The structure consists of single-unit-cell-thick ZIF-8 layers intercalated by the surfactant chains along the c direction. Although the precise position of the surfactant chains could not be determined due to limited data and likely due to disorder of the surfactant, they should occupy the interlayer spacing and intercalating the ZIF -layers.

[0106] Solid-state nuclear magnetic resonance (NMR) measurements also provided structural information of the ZIF-S material. Figure 2g showed the 'H solid-state NMR spectra of the ZIF-S-Zn material as compared to that of the two precursors (2-metylimidazole and SDS). Based on the proton and carbon chemical shifts and their correlation in theJH-13C HETCOR spectrum (Figure 2h), the peaks could be assigned as illustrated in Figure 2g. The material had a combination of peaksoriginating from both Hmlm and surfactant, which proves that the surfactant chains were incorporated in the structure. It is noted that theJH NMR spectrum for ZIF-S-Zn contains a -NH peak, which should not be a part of the ZIF material. Rather, it should come from unreacted Hmlm that was not washed out thoroughly. This was due to the fact that the ZIF-S could not be washed by solvent, otherwise it would either be dissolved (if using water) or transform to ZIF-8 (if using ethanol)). Moreover, aJH-JH EXSY solid-state NMR spectrum (Figure 2i) provided further information regarding the spatial proximities of the surfactant and the ligand incorporated in the framework. As depictured in Figure 2i, the correlation 1 suggested that the end group of the surfactant is a close neighbor of the imidazolium ring of the framework. Correlation 2 also suggested that the methyl group of the framework is in close proximity to the head group of the surfactant.

[0107] These results are consistent with the structure model and the expected charge-balancing electrostatic interactions between the dodecyl sulfate and the ZIF framework layer.

[0108] The characterization of the as-prepared ZIF-S-Co material of the invention showed that ZIF-S-Co nanosheets had morphology corresponding to a sheet with square morphology (Figure 3 a and b).

[0109] SAED revealed a square 2D lattice in the in-plane direction (Figure 3c). XRD and FTIR spectra confirmed that the structure is identical to that of the layered ZIF-S-Zn (Figure 3d and e). The layered ZIF-S-Co material also underwent topotactic condensation upon heat treatment above 200°C, changing from its layered structure to ZIF-67 structure as was confirmed by the in-situ XRD experiments (Figure 3f).

[0110] Scanning electron microscopy (SEM)

[0111] Scanning electron microscopy (SEM) images were collected using an FEI Teneo™ scanning electron microscope with Schottky Field Emission Gun at an acceleration voltage of 2 kV and inlens detector.

[0112] SEM samples of the ZIF materials were prepared by spreading the powdered material collected from centrifugation and drying on conductive carbon tape, followed by sputter-coating with ~ 5 nm thick Iridium layer before imaging to minimize sample charging effect. Transmission electron microscopy (TEM) images were collected using either an FEI Tecnai G2 Spirit™ transmission electron microscope with a LaB6 source at an acceleration voltage of 120 kV or a Talos F200S G2 Transmission Electron Microscope at an acceleration voltage of 200 kV. Focused-ion beam scanning electron microscopy (FIB-SEM) images were obtained using an FIB-SEM Zeiss CrossBeam 540. X-ray diffraction (XRD) patterns were recorded using a Bruker D8 Discover with CuKa radiation ( = 1.5406 A). Thermogravimetric analysis (TGA) was performed with a PerkinElmer TGA 8000 with heating and cooling rates of 1 °C / min. FUR (Fourier-transform infrared spectroscopy) measurements were performed on FT-IR-Spectrometer Spectrum Two (PerkinElmer) with an atmospheric vapor compensation feature (an advanced digital filtering algorithm) designed to compensate for CO2 and H2O absorptions in real time. Atomic force microscopy (AFM) images were collected using a Bruker MultiMode 8 AFM instrument.

[0113] Solid-state NMR

[0114] Solid-state NMR spectra of those samples collected from the synthesis mixture by centrifugation and drying were recorded on a 900 MHz Bruker wide bore spectrometer (21.1 T) equipped with an Avance Neo console. 'H Hahn echo NMR spectra and theJH-JH EXSY spectrum were recorded using a 1.3 mm HCDN quadruple resonance CPMAS probe while spinning the samples at 60 kHz.

[0115] 1H 7t / 2 and it pulses of 2.5 and 5 ps respectively were used for both ID and 2D experiments. Echo delays were set to two rotor periods (33 ps) and mixing time to 10 ms while applying radio-frequency-driven recoupling (RFDR) (Shen etal., 2012, Journal of Magnetic Resonance, 223, 107-119). 16 scans were sufficient to obtain a good signal-to-noise ratio for all the ID spectra and the EXSY experiment.

[0116] 13C CP (cross-polarization)

[0117] The13C CP (cross-polarization) and theJH-13C HETCOR spectra were recorded using a 3.2 mm HCN triple resonance CPMAS probe while spinning the sample at 20 kHz. The spectra were obtained by transferring polarization from 'H to13C to enhance the signal of the latter or to determine its proximity to protons while applying variable amplitude during the contact time of 1 ms (Peersen et al., 1993, J. Magn. Reson. A, 104, 334-339). 16384 transients were cumulated for the13C CP spectrum and 2048 transients were summed for each slice of the 2D correlation spectrum.

[0118] Samples were packed into 1.3 and 3.2 mm zirconia rotors and spun at 60 and 20 kHz respectively. Recovery delays were chosen to be 1.3 times the T 1 of protons, which was extracted from saturation recovery experiments.1H and13C chemical shifts were referenced relative to tetramethyl silane. Microcrystal Electron Diffraction (MicroED)

[0119] T = 100 K MicroED data were collected on an FEI Tecnai G2 Sphera™ equipped with a cheetah D detector with accelerating voltage 160 keV from Amsterdam Scientific. The crystals were cooled at liquid nitrogen temperature during the measurement using a Gatan cryoholder, to decrease radiation damage. Continuous rotation of the sample collected from the synthesis mixture by centrifugation and drying was applied for a maximum total rotation range of 25 degrees for eachcrystal. Data from 17 crystals were processed and merged using DIALS. Room temperature MicroED data were collected on an ELDICO ED-1 device (ELDICO Scientific AG) equipped with a QUADRO detector and a smart combination of a five-axis, 360° rotation, submicrometer-precise goniometer and a 160 keV electron beam. The structure could be solved using SHELXD3 in the space group P421m, showing a layered structure. The structure was refined in SHELXL.

[0120] Example 4: Topographic condensation of the synthesized layered ZIF materials according to the invention

[0121] The ability of the layered ZIF materials according to the invention to undergo topotactic condensation was investigated as layered zeolite precursors were described as being used to synthesize 3D frameworks by topotactic condensation (Marler et al., 2012, European Journal of Mineralogy, 24(3), 405-428; Chen et al., 2017, Crystal Growth & Design, 17(10), 5465-5473, Asakura et al., 2014. Chemistry A European Journal, 20(7), 1893-1900; Asakura et al., Dalton Transactions, 43(27), 10392-10395) . The as synthesized material was subjected to the following assay: powdered material collected from step f) of the method of the invention was loaded in a capillary and the capillary was mounted to the XRD machine (Bruker D8 Discover with CuKa radiation ( = 1.5406 A)). An external heating device was used to probe and control the temperature of the sample. XRD patterns of the sample was recorded at each preset temperatures (30°C, 100°C, 150°C, 180°C, 200°C, 250°C).

[0122] The material of the invention ZIF-S-Zn or ZIF-S-Co (both) also underwent topotactic condensation upon heat treatment. Figure 4 illustrates the phase change by topotactical condensation. The material maintained its layered structure at temperatures below 180°C. Upon heating to 200°C, the surfactant chains would decompose and the Zn-ZIF layers would condense to form the ZIF-8 structure, as evidenced by the in-situ XRD patterns measured at 200°C and 250°C. As opposed, ZIF-L could transform in ZIF-8 through a recrystallization process and not by topotactic condensation (Low, etal., 2014, Cryst. Growth Des., 14 (12), 6589-6598). Hydrothermal treatment was needed for a recrystallization process, whereas topotactic condensation can be induced solely by heat, which is economically advantageous and environmentally advantageous as does not produce liquid waste.

[0123] TGA study also suggested that the surfactant started to decompose at temperatures around 200°C (Figure 4d). This is in contrast with previously reported CTAB templated MIF-1 material, which did not show thermally induced phase transition. Rather, MIF-1 converted to poorly crystalline mesostructures upon heating (Junggeburth etal., 2012, supra). Morever, ZIF-S-Zn also transform to ZIF-8 upon ethanol washing at room temperature (Figure 5).Example 5: Preparation of membranes suitable for gas filtering systems

[0124] The as-synthesized layered material of the invention (e.g. ZIF-S-Zn or ZIF-S-Co), possessing a large lateral size and a high aspect ratio as characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), are attractive as building block for thin membranes. The suitability of the material for the preparation of thin membranes was tested as follows:

[0125] The suspension (supernatant) obtained in step f) of the method of the invention was kept static for 24 h to let thicker platelets settle down, the settled platelets having a thickness in the range of 40-60 nm (Figure 6a). Only the thinner platelets, referred to here as ZIF-S-Zn or ZIF-S-Co nanosheets with a thickness of approximately 10 nm (Figure 6b), remained in the suspension which were then used to deposit thin films (3 ml nanosheet suspension taken from the supernatant containing thinner nanosheets (-5-20 nm)) on a porous polybenzimidazole (PBI) support by a simple vacuum filtration through the PBI-AM support as reported in Duan et al., 2023, ACS Sustainable Chemistry & Engineering, 11(21), 8140-8147 or Duan etal., 2023, Journal of Membrane Science Letters, 3(1), 100045.

[0126] The PBI support was prepared beforehand by nonsolvent-induced phase separation as described in Dakhchoune et al., 2023, Journal of Membrane Science, 672, 121454. Briefly, a polymer dope solution having concentration of 8% (w / w) was prepared by adding commercial PBI-AM Fumion® powder in l-Methyl-2-pyrrolidinone (NMP) and mixing vigorously using mechanical stir. After stirring for overnight, the dope solution was centrifuged at 40,000 g-force for 3 hours to settle down any undissolved particles. PBI-AM films were casted on stainless-steel metal mesh using a doctor blade casting system. The as-cast films were coagulated in a 60°C deionized (DI) water bath for 9 hours to allow complete phase inversion and then washed thoroughly with deionized (DI) water before drying. Finally, the supports were dried at room temperature followed by heat treatment at 330°C for 8 hours with a heating and cooling rate of 0.5°C / min.

[0127] The PBI support host a smooth surface and an average pore size of approximately 20 nm (Figure 6d) The chemical compatibility of PBI and methylimidazole groups of the layers of the material of the invention makes these porous supports ideal for deposition of the nanosheets (of the material of the invention.

[0128] Upon application of vacuum filtration, the ZIF-S-Zn nanosheets deposited in oriented fashion, leading to a continuous thin film. Figure 6e showing the surface morphology of the as-prepared ZIF-S-Zn film after filtration on PBI supports, attests that compact and defect-less film wasprepared successfully. After filtration, the film was left in the vacuum filtration setup and dried under continuous vacuum suction.

[0129] The prepared PBI-AM support with the dried film was then sealed in a home-made filtration cell with Viton® gaskets and a filtration cell was prepared as described in Duan et al., 2023, ACS Sustainable Chemistry & Engineering, 11(21), 8140-8147.

[0130] Using the same membrane preparation protocol as was used for the ZIF-S-Zn case, compact and continuous ZIF-S-Co deposits could also be obtained. Figure 7a showed the AFM image of the thicker ZIF-S-Co platelets after centrifugation at 10’000 rpm for 10 min. They had a thickness of 60-80 nm. The solution was kept static for 24 h to remove most of the thicker platelets by sedimentation. Only thinner nanosheets, with thickness of -5-20 nm (Figure 7b), were used for membrane preparation. Figure 7d shows a typical SEM image of the as-prepared ZIF-S-Co membrane. The membrane appeared compact and continuous, with a thickness of approximately 300 nm as measured by cross-section prepared by focused ion beam (FIB) (Figure 7e).

[0131] Example 6: Gas filtering properties

[0132] Single gas and mixed gas permeation tests were performed using a permeation setup as reported earlier Duan etal., 2023, supra.

[0133] In the case of single gas permeation test, 30 mL single gas (EE, CO2, N2, or CH4) was fed to the membrane through the feed inlet. In the case of mixed gas permeation test, a 50 / 50 mol% gas mixture was fed to the membrane through the feed inlet. The pressure of feed was maintained at 2 bar. At the permeate side, Ar was used as the sweep gas and the pressure was kept at 1 bar. During test, the chemical potential difference would drive part of the feed gas through the membrane. The permeated gas would be removed by the sweep gas and sent to the mass spectrometer (Hiden Analytical, HPR-20) for a real time analysis. The steady state data was used to calculate the gas concentrations in permeate and further determine the gas permeances and membrane ideal selectivities and separation factors.

[0134] Single gas permeation tests were performed on the as-prepared ZIF-S-Zn nanosheet membrane to examine its molecular sieving properties. At room temperature, the membrane was impermeable to gases with permeance less than 10'12mol m'2s'1Pa'1. This was due to the presence of surfactant chains that blocked gas transport from the 4 membered rings (4-MR) constructed by the Zn node and Hmlm. When permeation temperature was increased to 150°C, membrane yielded a higher permeance, with EE permeance of 9 xIO'9mol m'2s'1Pa'1. The ZIF-S-Zn membrane yielded EE permeance of 2.2* 10'8mol m'2s'1pa'1at 200 °C and was selective to EE over CH4 and N2, but notCO2(Figure 6f) Ideal selectivities of H2with respect to CF and N2were 33 and 40, respectively. The H2 / CO2ideal selectivity was 5.

[0135] This suggests that the effective pore size is larger than the kinetic diameter of CO2(3.3 A), but smaller than that of CH4 (3.8 A) and N2(3.64 A). Upon further increasing the temperature to 200°C, the membrane showed an increased H2permeance of 2.2 *10'8mol m'2s'1Pa'1with ideal selectivities of H2with respect to N2and CH4 of 29.3 and 30, respectively.

[0136] Single gas permeation tests for ZIF-S-Co material showed similar trend as the case of ZIF-S-Zn membrane (Figure 7g). At room temperature, membrane had a low gas permeance due to blockage by surfactant chains. The membrane also showed increased gas transport with increasing temperature. For example, H2permeance increased to 9 *10'9mol m'2s'1Pa'1at 150°C and continued to increase to 2 *10'8mol m'2s'1Pa'1at 180°C and 3.1 *10'8mol m'2s'1Pa'1at 200°C. The ideal selectivities of H2over CO2, CPU and N2were close to 30, 400, and 200, respectively. This proves that the ZIF-S-Co membrane have more rigid 4-MR openings compared to that of the ZIF-S-Zn membrane. The effective pore opening in this case lies between the kinetic diameter of H2(2.89 A) and CO2(3.3 A), making the membrane selective for H2over CO2.

[0137] Example 7: Water vapor stability

[0138] One consideration of membranes for pre-combustion carbon capture is their stability under high temperature water vapor. To study the stability of ZIF-S-Co membranes under water vapor at high temperature, a TGA test was carried out under humidified atmosphere (~ 2.5 mol%). Powdered material collected from step f) of the method of the invention was loaded in a TGA Q55 instrument from TA Instruments. The instrumental setup was modified with a water bubbler to generate humidified atmosphere. Dry N2was supplied at a flow rate of 40 mL / min and merged with another N2stream that went through the water bubbler at a flow rate of 60 mL / min. The resulted N2stream contained water vapor with about 2.5% molar fraction and a flow rate of 100 mL / min.

[0139] Figure 7f shows that at 200 °C, the material is stable for the tested period (2 days). The weight loss at 200°C corresponds to the removal of surfactant chains. The stability of this membrane under humidified atmosphere was confirmed by a long-term membrane separation test at 200°C using a 50 / 50 mol% H2 / CO2mixture with ~ 1.5 mol% of water vapor. The test protocol is similar to the protocol described in Example 6 except that a water bubbler was add to the feed inlet to generate humidified atmosphere.Figure 7h demonstrated the membrane performed consistently even with the presence of water vapor. It showed a stable H2 permeance of 3.1><10'8mol m'2s'1Pa'1and corresponding H2 / CO2 separation factor close to 30.

[0140] Altogether those data support that a method of the invention allows to synthesize new layered ZIF structure (ZIF-S) templated by anionic surfactant chains (e.g. dodecyl sulfate ions). Depending on the metal source used, those can be obtained in Zn for Co form.

[0141] The structure of those materials solved by the micro-ED technique, shows single-unit-cell-thick layers formed by the ZIF sheets (e.g. ZIF-8 / ZIF-67) sheets intercalated by surfactant chains. A schematic representation of the structure can be found on Figure 2f.

[0142] Owing to the nanosheet morphology of this material, a facile vacuum filtration on porous supports could be used to prepare high-quality membranes.

[0143] Given the extremely facile method for membrane fabrication and the good separation performance, membranes made from a layered ZIF material according to the invention are highly promising for pre-combustion carbon capture.

[0144] Overall, this sheds light on the synthesis of new layered ZIF / MOF structure using anionic surfactants as a structure directing agent (SDA). With the diversity of anionic surfactant molecules and ZIF / MOF structures, development of novel layered ZIF / MOF material would be imagined, with applications not limited to membrane separation, but also catalysis, sensing, energy storage, electronic devices, drug delivery and other nanomaterial-based technologies.

[0145] Example 8: Preparation of further material of the invention

[0146] Further layered ZIF-67 have been prepared according to a method of the invention similarly as described in Example 1, except that the anionic surfactant solution of the metal precursor is added to the said organic ligand solution to form a reaction mixture wherein the molar ratio of Hmlm to metal is 36.

[0147] a) Providing an anionic surfactant in aqueous solution under continuous stirring Typically, an SDS solution was prepared by dissolving 0.18 g SDS in 100 mL ultrapure water (18.2 MQ cm) and mixed well by stirring.b) Providing a metal precursor solution and adding said metal precursor solution to the anionic surfactant in a molar ratio of metal ions to anionic surfactant from about 0.5 to about 4, , in particular from 0.5 to 2, under continuous stirring to form an anionic surfactant solution of the metal precursor

[0148] Then, 0.1572 g Co(NO3)2.6H2O was added into the SDS solution and the solution was mixed by stirring to form a SDS solution of Zn2+precursor or Co2+, respectively. In the present case, the molar ratio metal ions to anionic surfactant was 1:1.1.

[0149] c) Providing a separate organic ligand solution in aqueous solution under continuous stirring In parallel, an Hmlm solution was prepared by dissolving 1.6 g Hmlm in 100 mL ultrapure water (18.2 M cm) and mixed by stirring. The two solutions were kept stir at room temperature until homogenous. The molar ratio of Hmlm to metal being 36.

[0150] d) Adding the anionic surfactant solution of the metal precursor to the said organic ligand solution

[0151] Next, the SDS solutions of Co2+precursor were quickly added to the Hmlm solution. The molar ratio of the reactants was Co(NO3)2.6H2O : Hmlm : SDS = 1 : 36 : 1.1.

[0152] e) Leaving the formed mixture under stirring for a duration of 1 h until the mixture becomes cloudy and a layered ZIF is formed.

[0153] f) Collecting the obtained ZIF material

[0154] When the reaction was judged completed, the powdered ZIF materials (ZIF-S-Co) was retrieved by centrifuging at 10’000 rpm for 10 min and drying in a convection oven for about 12 h and stored. As can be seen on Figure 8, the same material as the one obtained under Example 1 was obtained. As a comparative example, a material was prepared according to a method of the invention wherein the molar ratio of metal ions to anionic surfactant is about 1 (as in Duan et al., 2023, supra, but with about 10 times lower precursor concentration) except that the molar ratio of Hmlm to metal is 8 (as in Duan et al., 2023, supra).

[0155] a) Providing an anionic surfactant in aqueous solution under continuous stirring Typically, an SDS solution was prepared by dissolving 0.115 g SDS in 100 mL ultrapure water (18.2 MQ cm) and mixed well by stirring.

[0156] b) Providing a metal precursor solution and adding said metal precursor solution to the anionic surfactant in a molar ratio of metal ions to anionic surfactant is about 1, under continuous stirring to form an anionic surfactant solution of the metal precursorThen, 0.116 g Co(NO3)2.6H2O was added into the SDS solution and the solution was mixed by stirring to form a SDS solution of Zn2+precursor or Co2+, respectively.

[0157] c) Providing a separate organic ligand solution in aqueous solution under continuous stirring In parallel, an Hmlm solution was prepared by dissolving 0.263 g Hmlm in 100 mL ultrapure water (18.2 MQ cm) and mixed by stirring. The two solutions were kept stir at room temperature until homogenous. The comparative molar ratio of Hmlm to metal being 8.

[0158] d) Adding the anionic surfactant solution of the metal precursor to the said organic ligand solution

[0159] Next, the SDS solutions of Co2+precursor were quickly added to the Hmlm solution. The molar ratio of the reactants was Co(NO3)2.6H2O : Hmlm : SDS = 1 : 8 : 1.

[0160] e) Leaving the formed mixture under stirring for a duration of 1 h until the mixture becomes cloudy.

[0161] f) Collecting the obtained ZIF material

[0162] When the reaction was judged completed, the powdered materials was retrieved by centrifuging at 10’000 rpm for 10 min and drying in a convection oven for about 12 h and stored.

[0163] As shown on Figure 9, the obtained material was different from the material of the invention in both morphology and structure. X-ray diffraction showed that the material is neither ZIF-67 nor the material of the invention (ZIF-S-Co). It is an unknown material with low crystallinity.

Claims

24Claims1. A method for the preparation of a layered Zeolitic imidazolate framework (ZIF) material, said method comprising the steps of:a) Providing an anionic surfactant solution of the metal ion precursor under continuous stirring wherein the molar ratio of metal ions to anionic surfactant is from about 0.5 to about 4 (e.g. typically from about 0.5 to about 2 such as from about 1 to about 2), under continuous stirring; b) Providing a separate organic ligand solution in aqueous solution under continuous stirring; c) Adding the anionic surfactant solution of the metal precursor to the said organic ligand solution to form a reaction mixture, wherein the molar ratio of organic ligand to the metal is from about 8.5 to about 150, from about 10-150, typically from 20-150, preferably from 30 to about 150, preferably by from 30-100, typically from 35-100;d) Leaving the formed mixture under stirring until a layered ZIF is formed;e) Collecting the obtained ZIF material.

2. A method according to claim 1, wherein the anionic surfactant is selected from Sodium dodecyl sulfate (SDS), Sodium lauryl ether sulfate, Sodium myreth sulfate, Sodium lauroyl sarcosinate, sodium dodecyl benzenesulfonate, and sodium stearate.

3. A method according to claim 1 or 2, wherein the organic ligand is selected from benzimidazolate and 2-methylimidazolate.

4. A method according to any one of claims 1 to 3, wherein the reaction mixture is left under continuous stirring until crystals with square and nanoplatelet morphology are formed which is indicative of the formation of layered ZIFs, typically from about 0.5 to 4 hours.

5. A method according to any one of claims 1 to 4, wherein the metal ions are selected from Zn2+and Co2+.

6. A method according to any one of claims 1 to 5, wherein the molar ratio of metal ions to anionic surfactant is from about 0.5 to about 2.

7. A two-dimensional layered ZIF material obtainable by a method according to any one of the preceding claims.

8. A two-dimensional layered ZIF material having a sheet-like morphology with an aspect ratio higher than 10, (e.g., 20-500 and a lateral size larger than 1’000 nm and which undergoes topotacticcondensation and forms its parent 3D ZIF material upon heating (e.g. to or above 200°C for ZIF-8 / ZIF-67).

9. A two-dimensional layered ZIF material according to claim 7 or 8 which structure comprises unit-cell-thick ZIF layers spaced by anionic surfactant micelles.

10. A two-dimensional layered ZIF material according to any one of claims 7 to 9 having a thickness of approximately 5-20 nm (e.g. 10 nm).

11. A two-dimensional layered ZIF material according to any one of claims 7 to 10 having a pore opening suitable for H2 / CO2 separation.

12. A two-dimensional layered ZIF material according to any one of claims 7 to 11, wherein the structure of the said two-dimensional layered ZIF material has the following unit cell parameters a = b = 16.82 A; c =24.5 A at room temperature.

13. A support, in particular a porous substrate coated with a film comprising a two-dimensional layered zeolitic imidazolate framework (ZIF) material according to any one of claims 7 to 12, in particular wherein the said film’s thickness is from about 100 nm to about 500 nm.

14. A selective gas filter comprising a membrane comprising a porous substrate coated with a two-dimensional layered ZIF film from a two-dimensional layered ZIF material according to any one of claims 7 to 12.

15. A selective gas filter according to claim 14, wherein the two-dimensional layered ZIF film’s pore aperture is from 0.29 nm to 0.33 nm at temperatures from 150°C to 200°C.

16. Use of a gas selective filter of claim 14 for separating H2 and CO2.

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